1. Field of the Invention
The present invention relates to a retaining structure of a brush spring of an electric motor which is designed to mount a brush spring only in a normal direction.
2. Description of the Prior Art
In conventional electric motors, as indicated in FIG. 5, a retainer 2 for holding a brush spring 1 is provided projecting on a support plate (not shown) of the motor at the lateral side of a guide means 4. A brush 3 generally in the form of a block is slidably supported by the guide means 4. The retainer 2 is generally columnar with a front end section thereof forked by an engaging groove 2a notched in an axial direction. The brush spring 1 is of the coil type and has its one end projecting outward from a coil portion 1c thereby to constitute a brush contact part 1a which is brought in contact with the brush 3 to urge the same, and the other end bending inward to the center of the coil portion 1c thereby to constitute an engaging part 1b which is engaged with the engaging groove 2a.
In mounting the brush spring 1 into the retainer 2, the coil portion 1c is first fitted in the exterior of the retainer 2, as indicated by a solid line in FIG. 5, such that the brush contact part 1a is positioned at the side opposite to the brush 3, and the engaging part 1b is engaged with the engaging groove 2a. Then, the contact part 1a is rotated in a direction shown by an arrow A as indicated by a chain line and inserted into a spring guide groove 4a formed in the guide means 4. Accordingly, the contact part 1a is brought into contact with an end face 3a of the brush 3, whereby the brush 3 is urged in a direction shown by an arrow B by the elastic rebound consequent to the torsion of the brush spring 1.
In the above-described process for mounting the brush spring 1, however, it may happen as is understood from FIG. 6 that the brush spring 1 is inadvertently mounted in the retainer 2 in a direction opposite to the normal direction, i.e., (rotated 180 degrees), and therefore the brush contact part 1a is positioned at the side of the brush 3 from the very start. This is because the engaging groove 2a of the retainer 2 is formed passing in a diametrical direction. In such state as above, since the brush spring 1 is hardly applied with a torsion, the urging force the brush 3 receives from the brush spring 1 is considerably smaller as compared when the brush spring 1 is mounted in the normal direction. Consequently, although the electric motor encounters no particular inconvenience at the start of use, it is brought to a halt in a short time when the brush 3 is worn out in a worsened sliding condition as a result of vibrations or the like. Even a slight rebound of the brush 3 will reduce the urging force of the brush spring 1, thereby stopping the electric motor.